Cathode for cathode ray tube



' Dec. 12, 1939. H. o. ROOSENASTEIN El" AL 2,132,831

CATHCDE FOR CATHODE RAY TUBE Filed March 24, 1937 i FfgL za. FialZhFQf-ZO 1 5441;. Mafia.

Fig.6e i

INVENTORS HANS o. ROOSENSTEIN KURT o EHLS BY ATTORNEY Patented Dec. 12,1939; it i e 1 W}. I v UNITED STATiEh i tFiiZ CATHODE' FOB CATHODE RAY TUBE Hans Otto Rcose'nstein and Kurt Diels, Berlin,

Germany, assignors to Teiefunken Gesellschaft fiir Drahtlose Telegraphic m. b. H, Berlin, Germany, a corporation of-Gerrnany '1 Application March '24, 1937, Serial No. 132,683 In Germany March 24, 1936 e 5 claims. 1(o1. 250-141 v This invention relates to electrondevices, and in Fig. 2c, the distribution of light inside a line, in 'particular, to electron emissive cathodes for inthe direction of its height, is no longer conuse in cathode rayapparatus. Stank-even not in a case where the number of Cathode fray devices have suffered in thepast electrons per .unit of area of the circular spot is 5 3 from the fact that where the cathode raybeam the same. To be sure, along the line marked. 5 I

developed in a cathode ray or Braun tube im- A+B, the current density is constant as shown pacts, upon a luminescent surface in a finely fcin Fig. 2b. The distribution of luminosity, how-,6 cused area, the illumination at the impact sur- ,ever, is subject to fluctuations in the direction face bounded by the cathode ray beam is not uniofthe height of a strip or line according to l form. Accordingly, it is one of the objects of semi-circle as shown in Fig.2c; The consequencethis invention to provide method and means for is that in the television picture, even if the lines producing a beam of electrons which, upon imare ,directly contiguous, in other words, when pact on a luminescentscreen or receiving electhey are' traced without any intervening spaces, trode, shall produce substantially uniform illurnia disturbing structure becomes noticeable in ver- 5 nation over elemental areas of the impact area. tical direction, in the presencecf zero module.- :1 Other and further objects will becomeappantion voltage. In actual practice, the conditions, ent upon the reading of the detailed description as a matter of fact, are even still more unsatistaken together with the drawingin which factory than shown in Fig. 20, for the reason Figs. 1a, 1b, 1c show-diagrammatically an aperthat, because of various factors, the current deni,

ture. of a Nipkow disk, graphi'callythe illuminasity throughout the-spot is not constant, but, de-

tion across the disk, and graphically the product creases somewhat inv marginal direction. of the elemental areas and the intensity of illucurrent density along lineC, D,'Fig. Eahas a mination' respectively, shapeas indicated in Fig. 3?) so that, the dis' Figs. 2a, 2b, and 2c show graphically the imtribution of the intensity over the height oil a' pact area of a cathode ray beam, the intensity line has a form as roughly indicated in Fig.

of illumination across the beam, and the prod- According to this invention, in order to avoid uct of elemental zones and intensity-ofillumihathese disadvantages, the specliic'electrcn emission j tion, respectively, I over the area or surface of the cathode is to be Figs. 3a, 3b and show graphically figures --chesen in such a way that the distribution of similar to those of Figs. 2a, 2b and 2c;for another light 'overtheheight or width of a line, becomes. type of cathode ray beam, at least approximately constant. In thecase of Figs. 4a., 4b and 40 show the spotarea, the ina distribution of emission along line EF, Fig. tensity and product of intensity, and elemental 4a, which is chosen approximately as show-n in areas respectively of an improved cathode ray Fig. 41), there results again-the desired constant.

3 beam in accordance with the invention, distribution as in Fig.'4=c I ,3 I

Fig. 5 shows the pin cushioning effect of a Presupposing a circular spot, and a roughly spot area from an uncorrected electronic lens, undistorting electron-optic lens, then the specific and electron'eznission of the cathode, i. 'e., the num-.-

Figs. 6a, 6b, and 6c showmodifications for the her of electrons emitted per unit area of the, I

Figs. 4a, 4b, and 4c; while cathode, inthe presence or" constant heating i0 Fig. 7c shows a modification of Fig.- 6c. rent, can be-so chosen that on the line marked Nipkow disks are known in the prior artin EF, Figmlo, the specific emission isvariable which the holes are of quadratic or. rectangular The aggregate emission of an area f to the total 7 form, with a view to rendering the brightness emission of surface area g must be inversely, v

45 or luminosity as constant as possible over the proportional to length L of area 1 to the length 45 ,1 width or height of a line or strip in a television M of area 9. This ruleholds good in the case frame. Fig. la shows a square opening of a where the fluorescence brightness is proportional Nipkow disk, Fig. 1b the intensity distribution 7 to the product of current density and. the tme in the vertical direction of an aperture, and Fig. during which this current density is acting. If a e 50.10 the brightness distribution h which is also fluorescent substance is used in which the fluo- 50,,

constant in vertical direction, of a line delineated rescence power, similarly as in photographic or traced with a Nipkow disk having quadratic p1ates,. for the same value of the said product openings. 1 decreases 'for a shorter time of action, the total In the case of Braun tubes in which the luemission striking surface f must be still greaterminous'spot-is circular .or roughly so, as shown Y than what results from the above rule. 55 I ent in the electron-optic lens.

ly quadratic.

A corresponding distribution of the electron emission throughout the area of a cathode is securable if the cathode surface, prior to its being mounted in a Braun tube, is subjected in an auxiliary device to an electron or ion bombardment across a shiftable slit disposed directly in front of the cathode, and if the length of such treatment of the cathode, and/or the intensity of the bombardment throughout the entire cathode surface is altered in such fashion that the electron emissive substance is partially destroyed.

In order to influence the intrinsic or surface brightness in the direction of the height or width of a line, in the sense of this invention,there could be used such delineation defects as may be pres- For example. an electron-optic lens with faulty delineation presenting cushion or pillow shape (with inward bulges or bays), in other words, a lens which produces a spot of the type shown in Fig. 5 from a quadratic cathode may be used under particularly simple conditions. Such an electron-optic lens, when used with a circular lens, would result in a pattern or image that is at least rough- Hence, in case of constant current density throughout the entire area of the fluorescent spot, constancy of surface brightness in the direction of the width of a line which is aimed at in the invention, could be attained to a greater degree than with an arrangement Fig. 2.

The requirement of invariable surface brilliance in the width of a line as contained in and solved by the invention could be combined with a further demand, namely, that the surface brilliance should be'still constant when the Braun tube, after having been mounted in a television receiver, has been turned while the position of the deflector coils has remained unaltered. Such a turn, as will be noted, may be necessary with a view to compensating inevitable dissymmetries in the construction and mounting of the tube' in reference to the terrestrial field or a constant field of the horizontal or vertical deflector coils. If the said additional demand is made, such auxiliary means as have been described in connection with Figs. 4 and 5 as can be readily seen are no longer applicable.

Hence, according to a further object of the invention the specific emissivity over the circular cathode surface is to be chosen in such a way that along each radius of the cathode surface the specific emissivity is made to rise in accordance with the same law in such a way that, for a circular spot, an at least approximately constant brilliance per unit area throughout the width of a strip or line is obtained. A determination of the corresponding electron emission distribution is feasible by analytic and graphic Ways and means, whence there results a curve such as shown in Fig. 612. A graphic determination is readily feasible inside an area amounting to percent of the spot diameter (cross-section), and thesame shows that within a distance, which amounts to 5 percent of the diameter the specific emission (or emissivity) must be of unity value (1), while in the middle of the circle it must be 0.21, while intermediately it must be subject to variations as shown. If in each surface element of the spot the emissivity is plotted in the direction of the third coordinate, there results a surface of rotation as will be seen. If the emission is chosen in accordance with Fig. 622, there ensues again a constant surface brilliance at least inside a stretch equal to 90% of the width or height of a line.

, inside the width of a line or strip roughly as indicated in Fig. 70. It can be readily seen that this shape must be obtained if the emission in the direction of the edge of the cathode surface is made to grow still more markedly than shown in Fig. 61). With such a larger surface brilliance at the upper and lower edge of the line or strip, even if consecutive lines or strips present a certain spacing or gap, the undesirable structure in the vertical sense of the picture can be caused to disappear to a still greater extent than with an arrangement as shown in Fig. 6.

In what precedes the assumption has been made that the cathode surface itself is imaged upon the fluorescent screen. But in a great many electron-optical arrangements this is true only in this sense that a real image of the cathode produced in the anode diaphragm in turn is thrown upon the fluorescent screen. However, this does not involve any essential change in the conditions suchas above outlined seeing that the current density inside a surface element of the real image is proportional to the emissivity of the corresponding surface element of thecathode.

In a finished Braun tube it is feasible to ascertain more exactly whether the brightness distribution throughout the height 01' width of a line or strip presents a roughly constant shape which is aimed at by this invention, by making the following test: If the defects caused byfaulty delineation of the electron-optic lens are not used, a line or strip of enlarged height is thrown upon the fluorescent screen While varying the By producing such a strip or line on the screen,

it will then be easy to ascertain whether the distribution of the surface brilliance according to this invention actually exists. Moreover, by the aid of a photo-optic objective a line or strip of normal delineation could be imaged enlarged and then the distribution of the surface brilliance could be checked up on this image. i

What we claim isz 1. A cathode for producing a concentrate beam of electrons in a cathode ray tube comprising a circular planar surface electron emitting element characterized by the fact that the ratio of specific electron emissivity at the peripheral zone on the circular surface bears a ratio of the order of 5 with respect to the specific electron emissivity at the center of the surface. 2. A cathode forproducing a concentrated beam of electrons in a cathode ray tube comprising a circular planar surface electron emitting element characterized by a varying specific electron emissivity throughout the area-of the element, and further characterized in that the product of the specific electron emissivity of any elemental zone of the element and the area of said elemental zone is substantially equal to the 1 product of the specific electron emissivity of any a a concentrated beam of electrons comprising a planar surface electron emitting element, said element comprising a plurality of contiguous elemental areas arranged according to a predetermined configuration, and each elemental area having difierent specific electron emissivity from that of contiguous areas.

4. An electron emitting cathode for producing a concentrated beam of electrons comprising a circular planar surface electron emitting element, said element having elemental zonal areas whose specific electron emissivity increases in proportion to the radial distance of the elemental area to the center of the element.

5. An electron emitting cathode for producing a concentrated beam of electrons comprising a circular planar surface electron emitting element, said element having a varying specific electron emissivity over the surface thereof with the specific electron emissivity progressively changing in accordance with the changes in the radial distance from the center to the periphery of the element.

KURT DIELS. HANS OTTO RQOSENSTEIN. 

